1. Field of the Invention
The present invention relates to active matrix image display devices using a current-driven luminescence element such as an organic electroluminescence (EL) element, and so on.
2. Description of the Related Art
Although organic EL elements represent the gray scale through current control, active matrix organic EL display devices have the problem that, due to variation in threshold voltage in drive transistors which drive the respective organic EL elements, luminance unevenness occurs even when the same signal voltage is provided to the pixels. Compensating the threshold voltage of the drive transistors of the organic EL elements is necessary for resolving luminance unevenness and producing an even screen. As a threshold voltage compensation circuit for suppressing variation in the threshold voltage of the drive transistors, there is a method of detecting the threshold voltage of a drive transistor by using four transistors per pixel (for example, see Non-Patent Reference 1: R. M. A. Dawson, et al, IEDM '98, Technical Digest, 1998, p. 875). Furthermore, there is a method of detecting the threshold voltage of a drive transistor by using three transistors per pixel, and scanning the voltage of a power source line (for example, see Patent Reference 1: Japanese Unexamined Patent Application Publication No. 2006-259374).